The present invention relates to a system for detecting defects in a displayed image. More specifically, the present invention relates to a system for detecting and correcting mura defects in a displayed image.
The number of liquid crystal displays, electroluminescent displays, organic light emitting devices, plasma displays, and other types of displays are increasing. The increasing demand for such displays has resulted in significant investments to create high quality production facilities to manufacture high quality displays.
Despite the significant investment, the display industry still primarily relies on the use of human operators to perform the final test and inspection of displays. The operator performs visual inspections of each display for defects, and accepts or rejects the display based upon the operator's perceptions. Such inspection includes, for example, pixel-based defects and area-based defects. The quality of the resulting inspection is dependent on the individual operator is inspection which are subjective and prone to error.
“Mura” defects are contrast-type defects, where one or more pixels is brighter or darker than surrounding pixels, when they should have uniform luminance. For example, when an intended flat region of color is displayed, various imperfections in the display components may result in undesirable modulations of the luminance. Mura defects may also be referred to as “Alluk” defects or generally non-uniformity distortions. Generically, such contrast-type defects may be identified as “blobs”, “bands”, “streaks”, etc. There are many stages in the manufacturing process that may result in Mura defects on the display.
Mura defects may appear as low frequency, high-frequency, noise-like, and/or very structured patterns on the display. In general, most Mura defects tend to be static in time once a display is constructed. However, some Mura defects that are time dependent include pixel defects as well as various types of non-uniform aging, yellowing, and burn in. Display non-uniformity deviations that are due to the input signal (such as image capture noise) are not considered Mura defects.
Referring to FIG. 1, mura defects may occur as a result of various components of the display. The combination of the light sources (e.g., fluorescent tubes or light emitting diodes) and the diffuser results in very low frequency modulations as opposed to a uniform field in the resulting displayed image. The LCD panel itself may be a source of mura defects because of non-uniformity in the liquid crystal material deposited on the glass. This type of mura tends to be low frequency with strong asymmetry, that is, it may appear streaky which has some higher frequency components in a single direction. Another source of mura defects tends to be the driving circuitry (e.g., clocking noise) which causes grid like distortions on the display. Yet another source of mura defects is pixel noise, which is primarily due to variations in the localized driving circuitry (e.g., the thin film transistors) and is usually manifested as a fixed pattern noise.
What is needed is improved Mura reduction techniques.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.